[Qemu-devel] [PATCH 1/2] qcow2: Correct bitmap size in zero expansion

[Max Reitz]

Since the expanded_clusters bitmap is addressed using host offsets in
the underlying image file, the correct size to use for allocating the
bitmap is not determined by the guest disk image but by the underlying
host image file.

Furthermore, this size may change during the expansion due to cluster
allocations on growable image files. In this case, the bitmap needs to
be resized as well to reflect the growth.

Signed-off-by: Max Reitz <address@hidden>
---
 block/qcow2-cluster.c | 38 +++++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 738ff73..a8e17f1 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1509,8 +1509,8 @@ fail:
  * i.e., the number of bits in expanded_clusters.
  */
 static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t *l1_table,
-                                      int l1_size, uint8_t *expanded_clusters,
-                                      uint64_t nb_clusters)
+                                      int l1_size, uint8_t **expanded_clusters,
+                                      uint64_t *nb_clusters)
 {
     BDRVQcowState *s = bs->opaque;
     bool is_active_l1 = (l1_table == s->l1_table);
@@ -1553,8 +1553,8 @@ static int expand_zero_clusters_in_l1(BlockDriverState 
*bs, uint64_t *l1_table,
 
             if (cluster_type == QCOW2_CLUSTER_NORMAL) {
                 cluster_index = offset >> s->cluster_bits;
-                assert((cluster_index >= 0) && (cluster_index < nb_clusters));
-                if (expanded_clusters[cluster_index / 8] &
+                assert((cluster_index >= 0) && (cluster_index < *nb_clusters));
+                if ((*expanded_clusters)[cluster_index / 8] &
                     (1 << (cluster_index % 8))) {
                     /* Probably a shared L2 table; this cluster was a zero
                      * cluster which has been expanded, its refcount
@@ -1612,8 +1612,25 @@ static int expand_zero_clusters_in_l1(BlockDriverState 
*bs, uint64_t *l1_table,
             l2_dirty = true;
 
             cluster_index = offset >> s->cluster_bits;
-            assert((cluster_index >= 0) && (cluster_index < nb_clusters));
-            expanded_clusters[cluster_index / 8] |= 1 << (cluster_index % 8);
+
+            if (cluster_index >= *nb_clusters) {
+                uint64_t old_bitmap_size = (*nb_clusters + 7) / 8;
+                uint64_t new_bitmap_size;
+                /* The offset may lie beyond the old end of the underlying 
image
+                 * file for growable files only */
+                assert(bs->file->growable);
+                *nb_clusters = size_to_clusters(s, bs->file->total_sectors *
+                                                BDRV_SECTOR_SIZE);
+                new_bitmap_size = (*nb_clusters + 7) / 8;
+                *expanded_clusters = g_realloc(*expanded_clusters,
+                                               new_bitmap_size);
+                /* clear the newly allocated space */
+                memset(&(*expanded_clusters)[old_bitmap_size], 0,
+                       new_bitmap_size - old_bitmap_size);
+            }
+
+            assert((cluster_index >= 0) && (cluster_index < *nb_clusters));
+            (*expanded_clusters)[cluster_index / 8] |= 1 << (cluster_index % 
8);
         }
 
         if (is_active_l1) {
@@ -1672,18 +1689,17 @@ int qcow2_expand_zero_clusters(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
     uint64_t *l1_table = NULL;
-    int cluster_to_sector_bits = s->cluster_bits - BDRV_SECTOR_BITS;
     uint64_t nb_clusters;
     uint8_t *expanded_clusters;
     int ret;
     int i, j;
 
-    nb_clusters = (bs->total_sectors + (1 << cluster_to_sector_bits) - 1)
-            >> cluster_to_sector_bits;
+    nb_clusters = size_to_clusters(s, bs->file->total_sectors *
+                                   BDRV_SECTOR_SIZE);
     expanded_clusters = g_malloc0((nb_clusters + 7) / 8);
 
     ret = expand_zero_clusters_in_l1(bs, s->l1_table, s->l1_size,
-                                     expanded_clusters, nb_clusters);
+                                     &expanded_clusters, &nb_clusters);
     if (ret < 0) {
         goto fail;
     }
@@ -1717,7 +1733,7 @@ int qcow2_expand_zero_clusters(BlockDriverState *bs)
         }
 
         ret = expand_zero_clusters_in_l1(bs, l1_table, s->snapshots[i].l1_size,
-                                         expanded_clusters, nb_clusters);
+                                         &expanded_clusters, &nb_clusters);
         if (ret < 0) {
             goto fail;
         }
-- 
1.8.3.1